Aberrant conductive pathways can develop in heart tissue and the surrounding tissue, disrupting the normal path of the heart's electrical impulses. For example, conduction blocks can cause the electrical impulse to degenerate into several circular wavelets that disrupt the normal activation of the atria or ventricles. The aberrant conductive pathways create abnormal, irregular, and sometimes life-threatening heart rhythms called arrhythmias.
Ablation is one way of treating arrhythmias and restoring normal contraction. One ablation technique is radio frequency (RF) ablation. The sources of the aberrant pathways, referred to as focal arrhythmia substrates, are located and then destroyed or ablated. Extra electrical pathways, which may trigger an atrial arrhythmia, may be formed at the base or within one or more pulmonary veins. To treat such an aberration, physicians may use multiple catheters to gain access into interior regions of the pulmonary vein tissue for mapping and ablating targeted tissue areas. The process is referred to as pulmonary vein (PV) isolation. A mapping catheter can be used to map the aberrant conductive pathway within the pulmonary vein. A physician introduces the mapping catheter through a main vein, typically the femoral vein, and into the interior region of the pulmonary vein that is to be treated. The antrum or the ostium of the PV is mapped at the beginning of the procedure. Based on this electrical mapping potential foci for the arrhythmia are identified.
An introducer guide sheath or guide wire may be used to place the mapping catheter within the vasculature of the patient. The introducer guide sheath is introduced into the left atrium of the heart using a conventional retrograde approach, i.e., through the respective aortic and mitral valves of the heart. Alternatively, the introducer guide sheath may be introduced into the left atrium using a transeptal approach, i.e., through the atrial septum. In either method, the catheter is introduced through the introducer guide sheath until a probe assembly at a distal portion of the catheter resides within the left atrium. Once inside the left atrium, the physician may deliver the probe assembly into a desired pulmonary vein using a steering mechanism. The physician situates the probe assembly within a selected tissue region in the interior of the pulmonary vein, adjacent to the opening into the left atrium, and maps electrical activity in the pulmonary vein tissue using one or more electrodes of the probe assembly. After mapping, the physician may introduce an ablation catheter to ablate the aberrant tissue using an ablation electrode carried on the distal tip of the ablation catheter to the interior of the pulmonary vein. The ablation electrode is placed in direct contact with the tissue that is to be ablated. The physician directs RF energy from the ablation electrode through tissue to ablate the tissue and form a lesion.
FIGS. 1A-1B illustrate a known mapping catheter with a catheter body 101 generally tangential to a loop-shaped probe assembly 102 and orthogonal to a loop plane 103 for the loop-shaped probe assembly 102. This design is relatively small. The probe assembly is a generally tubular structure, which is formed into the loop shape for the probe assembly. The diameter of the tubular structure is on the order of 3½ Fr (1.2 mm). However, this design provides challenges for maintaining a stable orientation to perform the mapping.